The present invention relates to an alignment disk for a magnetic disk driving apparatus which enables high precision tracking when a head carriage drive of the magnetic disk driving apparatus is positioned to a predetermined position along a track diameter, and particularly when a drive of a magnetic disk having a bit density of more than 96 or 100 tracks per inch (TPI) is positioned, and to method and apparatus for verifying a tracking error of the magnetic disk driving apparatus.
A prior art alignment disk is explained. JP-B-59-7142 discloses an example of the prior art alignment disk. An index mark and a track diametric positioning signal are recorded on the disk. The positioning signal of the alignment disk is supplied to a magnetic disk driving apparatus, reproduced by a magnetic head and displayed on an osciloscope. In this manner, the track diametric positioning is attained.
However, the above prior art alignment disk does not have all of a track diameter adjust signal, index timing adjust signal and azimuth adjust signal, which are necessary for data interchangeability. The adjustment by the osciloscope is of low resolution and assures the data interchangeability between magnetic disk driving apparatuses of a class of 48 PTI, but it is hard to assure the data compatibility between the magnetic disk driving apparatuses of a higher bit density, i.e. 96 TPI or 100 TPI.
Another example of the prior art alignment disk is explained with reference to FIG. 1. An index timing adjust signal 21 is provided on an outer track of an alignment disk 1. A track diameter adjust signal 36 is provided on a center track between an inner track and the outer track. The signal 36 comprises a larger diameter signal 37 which is eccentric from a center of rotation 2 by a predetermined distance .epsilon.=0.1 mm and larger than a reference diameter by .delta./2=0.075 mm, and a smaller diameter signal 38 which is also eccentric from the center of rotation 2 by the distance s and smaller than the reference diameter by .delta./2. These signals 37 and 38 are detected by a so-called cat eye signal. A CW (clockwise) signal 31 and a CCW (counter clockwise) signal 32 are provided on the inner track as an azimuth adjust signal 30. The same signals are recorded on a back side of the alignment disk 1 so that two upper and lower heads are tracked.
In the tracking adjustment by using the alignment disk, the alignment disk 1 is loaded to the magnetic disk driving apparatus, a head carriage is moved to a particular track of the disk, and the adjust signals are reproduced and displayed on the osciloscope.
In the index timing adjust, a time period T from an index timing detection point IDX to the index timing adjust signal 21 is measured, and the position of the index detection sensor is adjusted such that the time period T is within a predetermined period.
In the track diameter adjustment, the stepping motor is finely adjusted such that output voltages of the larger diameter signal 37 and the smaller diameter signal 38 become the same. In the azimuth adjustment, the head inclination is adjusted such that a ratio of the four signals 31 and 32 is within a predetermined range.
By using the above alignment disk, the index timing adjustment and the azimuth detection of the magnetic disk driving apparatus are attained. However, the resolution attained by the track diameter adjustment by the cat eye signal is low and it is hard to assure the data interchangeability of the driving apparatus the high density magnetic disk such as 96 TPI or 100 TPI.
Further, it is not possible to determine a chucking error based on a format of the reproduced signal.
The data interchangeability of the high density magnetic disk driving apparatus is now explained. Because there are a plurality of magnetic disk driving apparatuses on which magnetic disks are loaded and unloaded record and reproduce data, there is an error (called an off-track) between a predetermined track diametric position on the disk and an actual position at which the magnetic head is positioned by the magnetic disk driving apparatus. Major causes therefor are:
(1) Position adjust error of the carriage. PA1 (2) Positioning error of the carriage. PA1 (3) Chucking error (eccentricity) caused when the magnetic disk is chucked to the magnetic disk driving apparatus. PA1 (4) Difference in expansion and shrinkage of the magnetic disk and the magnetic disk driving apparatus by temperature and humidity change.
As to the index timing and the azimuth, there are also errors between two magnetic disk driving apparatuses.
In the 96 TPI magnetic disk driving apparatus a tolerance X of the off-track relates to a magnetic head R/W gap width W=165 .mu.m and an erase core width E.sub.r =100 .mu.m, and X is approximately 50 .mu.m. The tolerance X=50 .mu.m is distributed into the error items (1) to (4) so that the total of the errors of the items (1) to (4) is within 50 .mu.m, in order to assure the data interchangeability. However, the expansion/shrinkage error by the temperature and humidity in the item (4) is hard to reduce because of a large affect by a property of matter of the material.
The error items (1) to (3) are analyzed.
(1) The carriage position adjust error is an error caused when the head and a carriage transmission system are assembled into the carriage. This error closely relates to the assemble and adjust time. In order to reduce the error, the adjust time must be significantly lengthened.
(2) The carriage positioning error is caused by a stepping motor (STM) positioning error due to precision errors of parts of the STM and its drive system, and a positioning error due to precision errors of parts of the STM drive force transmission system. However, in the drive of the high density magnetic disk, the manufacturing precisions of the STM, drive system and transmission system have reached the limits, and if the precision is to be more improved, the yield is reduced, which will lead to the cost increase and quality instability.
(3) Major causes of the chucking error are a precision of parts of the chuck unit of the magnetic disk, and a precision of parts of the chucking unit of the magnetic disk driving apparatus. The precision of the parts in the high density magnetic disk driving apparatus reached its limit, and if the precision is to be improved, the yield is reduced which leads to the increase of cost and the instability of quality.
As described above, in the high density magnetic disk driving apparatus, the precision for the components is at their limits, and in order to assure the data interchangeability between the magnetic disk driving apparatuses on which a plurality of disks are loaded and unloaded, it is necessary to improve the precision of components which leads to the cost increase, or to improve the precision of the position adjustment of the head carriage driver. Those cause problems in the manufacturing efficiency and reliability.
In the prior art apparatus, the positioning error of the stepping motor, hysteresis error and accumulated error of the transmission system, which are to be detected in the tracking adjustment to assure the data interchangeability, are not detected as a result, the off-track increase in the tracks other than the adjusted track or in the innermost and outermost tracks and the read/write error occurs. Further, the prior art apparatus cannot measure the chucking error between the magnetic disk driving apparatus and the magnetic recording medium, and the off-track increases by the eccentricity due to the chucking error and the tracking error occurs.